Tribological behaviour at room temperature and at 550°C of TiC-based plasma sprayed coatings in fretting gross slip conditions

This paper deals with the investigation of the tribological behaviour of cermet plasma sprayed coatings in fretting conditions. Low pressure plasma sprayed NiCrFeAlTi-TiC, NiCr-(Ti, Ta)C and NiCrMo-(Ti, Ta)C coatings were tested at room temperature and at 550°C, against sapphire ball under gross slip conditions. Air plasma sprayed NiCr and NiCr-TiC coatings, as well as the high velocity oxy-fuel WC-Co coating, were investigated for comparison with the coatings tested in the present study. The coatings were classified with respect to wear and friction behaviour. The matrix and the carbide modifications of the NiCr-TiC coating influenced positively the coating wear and friction behaviour. The wear resistance of all the coatings decreased at high temperature. The NiCrFeAlTi-TiC coating showed the best wear resistance among the TiC-based coatings. At room temperature and at 550°C, the WC-Co coating was more wear resistant than the TiC-based coatings, eventhough the coating cracked in the high temperature tests. The coefficients of friction (COFs) of the WC-Co coating, tested against sapphire, were lower than the COFs of the TiC-based coatings at room temperature, but not at 550°C. XRD and SEM investigation of the wear tracks gave information on the active wear mechanisms.